Particular problems exist with operating switches in relatively high voltage environments. For example, in a mechanical switch, arcing can occur on opening, in which ionisation of the air between separating contacts allows the air to act as a conductor. This is potentially dangerous in itself and also causes wear to the equipment, which therefore requires regular review and renewal.
Solid state switches (i.e. semiconductor switches such as Integrated Gate Bipolar Transistors (IGBTs), Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETS), and the like) do not suffer from arcing, but currently available solid state switches are not generally able to support the full voltage of a relatively high voltage environment and/or switches which can support higher voltages are expensive. This means that, where they are used in a high voltage environment, it is usual to provide several (in some example up to a hundred or more) solid state switching elements connected in series to provide a switch.
In such a series connection, there is usually a need to balance or share voltages over a series connections of switching elements to ensure that no one switching element is required to support in excess of the maximum voltage allowed voltage for that switching element (the maximum voltage advised is known as the ‘voltage rating’ of the switching element), usually by ensuring that the voltage supported is equal or close to equal across all the switching elements in the series connection.